SEOUL (Yonhap) -- North Korea has again temporarily designated two areas near the western maritime border with South Korea as "naval firing zones," raising the possibility of further artillery shelling in the Yellow Sea, informed sources said Feb. 3.

Last week, North Korea fired a barrage of artillery shells into waters just north of the NLL over a period of three days beginning on Jan. 27, two days after unilateral declaration of "no-sail" zones in the waters near two South Korean islands.

The additional designation of naval firing zones was disclosed at the National Assembly. During a government-ruling party meeting held at the parliament, senior Defense Ministry officials briefed lawmakers that the North has designated an additional four-day "naval firing period" for the two zones -- east of the islands of Baengnyeong and Daecheong -- effective from Feb. 5, according to sources privy to the meeting.

The officials said the North may show further provocations considering the redesignation of the naval firing zone.

As part of its regular military drill, North Korea last week declared the two areas near the Northern Limit Line (NLL), the de facto maritime borer, in the Yellow Sea as naval firing zones from Jan. 25-29 during which it fired some 350 artillery shells into the zones.

The country also declared five additional no-sail zones over the weekend. According to South Korean military sources on Feb. 1, North Korea declared five additional maritime areas off the country's east and west coasts as "no-sail" zones over the weekend, raising concerns over the possibility of a short-range missile launch.

The move, taken on Jan. 31, followed the North's declaration on Jan. 25 of two maritime areas near the Northern Limit Line (NLL) in the Yellow Sea as "no-sail" zones until March 29, the last day of the country's "regular" military drills.

The NLL, the de facto inter-Korean maritime border, was drawn by the U.S.-led U.N. Command at the end of the Korean War and the communist North has refused to honor it. The two sides fought bloody skirmishes near the border in 1999, 2002 and in November last year.

The additional zones include western waters off the South Korean island of Gyodong and the coasts of the North Korean counties of Cholsan and Sonchon in North Pyongan Province and eastern waters off the coast of Kumya county in South Hamgyong Province, the sources said.

The communist country originally effectuated the no-sail zones at 7:00 a.m.-8 p.m. between Jan. 31-Feb. 1, and then extended them for another day, according to the sources. The South's military was reportedly monitoring for signs the North might fire a short-range missile. The North has occasionally fired missiles into seas off the coasts of the Cholsan, Sonchon and Kumya counties.

Last October, North Korea fired short-range missiles off its east coast as the latest in a series of weapons tests that included the May detonation of its second nuclear device. The communist state then pulled out of the six-party denuclearization talks after the United Nations imposed sanctions on Pyongyang for the nuclear tests and the April long-range rocket launch.

South Korea's military is keeping tabs on the possibility of additional artillery shell firings by North Korea near an inter-Korea sea border. "We are maintaining readiness for countermeasures as there could possibly be additional firing of artillery," a military official, requesting anonymity, said.

The South Korean military has detected several instances of "faint gunfire sound" in the North's region north of Yeonpyeong Island, according to the official. Yeonpyeong Island is located about 80 kilometers west of the northernmost end of South Korea's mainland and 12km from the North.

Due to its proximity to North Korea and waters rich in fish, the island has been a point of high tension between the divided countries. Naval skirmishes occurred in nearby waters in 1999, 2002 and November last year.

Analysts here say the latest provocations by Pyongyang indicate an attempt to increase its leverage as it prepares to return to six-party denuclearization-for-aid talks, which include South Korea, the United States, Japan, Russia and China.

Although the North has yet to actually return, diplomatic sources in Seoul said it was time to restart the talks. They also said sizable incentives would be offered for denuclearization.

The North also showed a conciliatory gesture toward the United States amid the barrage of artillery shells. In a contradictory move on Jan. 27, the day of the first round of shootings, the North conveyed to the United Nations Command its wishes to resume the joint excavation work with the U.S. to uncover the remains of American soldiers killed in the Korean War.

The work had helped uncover some 200 bodies since 1996, but was halted in 2005 for security reasons cited by Washington.

The regular North Korean policy featuring the combination of reconciliatory and provocative gestures triggered speculation that Pyongyang is again seeking increased leverage for reaping both economic and diplomatic benefits.

"We see this as typical North Korean behavior. It usually alternates between saber rattling and reconciliatory moves before it makes a big diplomatic decision," said Won Tae-jae, the Defense Ministry spokesman. He added that the North also may be seeking to strengthen its military morale after it was defeated by the South Korean Navy last year in a marine skirmish.